A normalization group lets you define a group of targets that will have the sum of their weights normalized to 1.0 as you edit them using the Paint Blend Shape Weights Tool. See also Paint blend shape deformer weights.
To create a normalization group
The Edit Normalization Groups window lists all blend shapes in the current scene.
(For example, if you have three blend shapes listed, you can enter 1 next to the first target to assign it to group 1, and enter 2 next to the following two targets to add them both to normalization group 2.)
After you create normalization groups, they appear as new paintable targets in the Paint Blend Shape Weights Tool.